1. Field of the Invention
The present invention concerns a method of making a component consisting of a support and a membrane welded thereto. The invention is more specifically concerned with a method of making a component consisting of a substantially cylindrical support through which there is a substantially coaxial orifice and a membrane welded to one end of the cylinder. The present invention also concerns a membrane-supports assembly obtained during execution of the method.
One embodiment of the invention relates, more particularly, to a method of making a plug for a straw, consisting of a substantially cylindrical insert, through which there is a substantially coaxial orifice, and a microporous hydrophobic membrane which is impervious to liquids and impermeable to gases and is welded to one end of the cylinder, and to a microporous hydrophobic membrane/inserts assembly obtained during execution of the method.
2. Description of the Prior Art
Straws for conservation of small quantities of substances, in particular biological substances, especially biological liquids, are known as xe2x80x9cFrench strawsxe2x80x9d and were disclosed for the first time in French patent No. 995 878.
The straws had a three-part plug consisting of two stoppers made from a fibrous substance with between them a powder adapted to be converted on contact with a liquid into an impermeable gel or paste adhering to the wall of the tube to create a sealed stopper.
Straws with a three-part stopper developed and sold by the assignees of the applicants are entirely satisfactory. Nevertheless, very slight absorption of the liquid contained in the straw has been noted.
There are also small three-part stoppers, but this solution does not solve the problem of absorption either.
One proposed solution to the above problem is to replace the three-part stopper with a rigid plastic material or metal ball. This solution has not proved satisfactory because, although it eliminates absorption of the liquid contained in the straw, new and unacceptable problems have arisen, the stopper no longer being at all impervious to liquids.
The assignees of the applicants have developed a straw with a two-part stopper that does not suffer from the above drawbacks.
In their French patent application FR 97 14729, the assignees of the applicants describe a straw for the conservation of small quantities of substances, in particular biological substances, comprising a segment of tube having closure means inside one end thereof, characterized in that said closure means comprise a two-part stopper consisting of a microporous and hydrophobic membrane and an insert through which there is a substantially coaxial orifice. According to one feature of the above patent application, the membrane is substantially perpendicular to the longitudinal axis of a substantially cylindrical insert welded to the membrane.
The present invention proposes a method of making a stopper of the above kind comprising a substantially cylindrical insert through which there is a substantially coaxial orifice and a microporous and hydrophobic membrane which is impervious to liquids but permeable to gases welded to one end of the cylinder.
The invention is more generally concerned with making a component consisting of a substantially cylindrical support through which there is a substantially coaxial orifice and a membrane welded to one end of the cylinder and substantially perpendicular to the longitudinal axis of the support.
The present invention can be used to make two-part stoppers for straws and filter elements.
In the case of a stopper comprising an insert and a membrane welded to it, the support of the membrane is an insert and the membrane is microporous and hydrophobic, impervious to liquids and permeable to gases, and in the case of a filter element, the support is a ring and the membrane is a filter medium.
In accordance with the present invention, a substantially plane membrane is thermally welded to a support substantially perpendicularly to the longitudinal axis of the support and the support is torn off the membrane in a direction substantially perpendicular to the plane of the membrane.
The membrane is welded to the support by means of a die having a shape such that after cooling the support can be torn off the membrane.
At the time of the thermal welding, a pre-cut of the membrane is formed, enabling it to be torn without burrs.
For example, a heating electrode is used whose shape pre-cuts the membrane to enable it to be torn off without burrs.
To tear the support off, the membrane is held in place or the support is trapped by means of a stripper and traction is applied substantially perpendicularly to the plane of the membrane. In this case, a stripper plate bears on the membrane. The support is pulled off with pliers or a holding tool by applying traction substantially perpendicularly to the plane of the membrane.
One solution which avoids the use of a stripper is to use a suction plate, i.e. a plate having a plurality of orifices, connected to a vacuum pump. The membrane-supports assembly is placed on the plate and suction is applied. Tearing off is achieved under the same conditions as previously.
The membrane is welded to the support by means of a welding anvil having an electrode at one end, for example. In one embodiment of the method of the invention the electrode is rotated by an amount between a fraction of a turn and several turns, for example one half-turn, which facilitates tearing off by encouraging the onset of rupture between the membrane and the support.
The combination of welding and tearing in accordance with the invention avoids the need for punching after welding.
In practise, an assembly is first made comprising the membrane and a plurality of supports, the plane of the membrane being substantially perpendicular to the longitudinal axes of the supports.
The membrane can be a filter membrane, for example, and can be hydrophobic.
In the case of a stopper for a straw, as mentioned above, the membrane is microporous, hydrophobic, impervious to liquids and permeable to gases.
The microporous membrane used preferably has a pore diameter in the range from approximately 0.001 xcexcm to approximately 10 xcexcm and the diameter of the pores of the membrane is more preferably less than or equal to 0.2 xcexcm. The membrane is made from a polymer material, for example a material chosen from high-density polyethylene (PE-HD), polyamide, nitrocellulose, polyester, phenol-formol resin (PF resin), perfluoroalkoxy resin (PFA) and fluorocarbon resin.
The polymer material of the membrane advantageously has a bubble point P greater than 6.105 Pa (6 bars) at 0.2 xcexcm.
When making a stopper for a straw, the insert is usually made of a material chosen from an elastomer material, a thermoplastics material and a thermoplastics elastomer material. The insert is advantageously made of polyethylene.
In one embodiment of the invention, the material of the insert is colored. This provides a xe2x80x9ccolor codexe2x80x9d without the need to use colored straws.
The present invention will now be described in more detail, by way of non-limiting example and with reference to the accompanying drawings, which show the making of a two-part stopper for a straw, in the form of an insert welded to a filter membrane.